Articles of produce such as apples and citrus fruit usually are inspected as part of a commercial packing operation. This inspection may include viewing each article for color or other visual information indicating variable factors such as the degree of ripeness, the size or volume of the article, the shape of the article, and any blemishes or other local discolorations on the surface of the article. Articles such as grapefruit and oranges, for example, may be graded for sale as table-grade fruit, as suitable only for juicing, or to be thrown away as unacceptable, depending on the exterior appearance or other factors of each article.
Perhaps the simplest way to accomplish surface inspection of fruit is by human visual inspection of each article. The manpower requirements and resulting expense of human inspection for each article of fruit, the incompatibility of such inspection with the article throughput speeds available from other components of modern commercial packing house equipment, and the desire to grade each article to an objective standard, all emphasize the need for effective alternative solutions to the problem.
It has become known in the art to electronically scan articles such as fruit and to apply signal-processing techniques for evaluating the resulting scanned signals. For example, it is known in the art to position one or more video cameras that can scan articles of fruit and produce electronic signals corresponding to that scan. Those scanning signals are processed to provide information on factors such as the color, shape, or lack of uniform color of each article, as seen by the camera. Conventional video cameras or cameras utilizing photodiode arrays are proposed in the prior art for visual inspection of fruit. Various signal-processing algorithms or techniques can compare the measured signals for each article against predetermined signals corresponding to desired standards for the factors, thereby producing a objective grading standard for each inspected article.
The quality of grading produced by such optical inspection of fruit requires viewing substantially the entire surface of each article. For generally round articles such as grapefruit, successive articles are supported on rollers or wheels and conveyed single-file through an inspection station containing one or more video cameras. The rollers or wheels supporting each individual article are caused to rotate while conveying that article through the inspection station, in an effort to present all portions of the article by turning the article for scanning by the camera or cameras. However, a piece of fruit that is not round may slip as the rollers attempt to turn the piece, leaving part of the fruit unexposed to the camera.
Furthermore, the best results of such optical scanning are obtained by scanning each portion of the article substantially perpendicular to the boresight or optical axis of scan. For example, a single video camera positioned alongside a conveyor will see approximately one hemisphere of each grapefruit moving along that conveyor. However, the amount of usable information in the resulting video signal is best at the surface portions viewed head-on by the camera, that is, those portions at or nearly perpendicular to the optical axis of the camera. The quality of visual information obtained from that view becomes degraded due to optical foreshortening and imperfections at outer diameters of the camera lens, for portions of the fruit increasingly remote form the optical axis, i.e., near the outer regions of the hemisphere being viewed. Imperfections such as non-uniform color occurring near those outermost regions of view, may be missing from the video information produced by one or two cameras viewing an article moving between two opposed cameras, with the inspection techniques known in the prior art.